Over 4 million adults are living with a total knee replacement (TKR); however, most do not achieve
recommended physical activity levels. To date, physical activity interventions for adults with TKR have primarily
been intensive, in-person, and costly interventions. However, given the barriers associated with these intensive
programs (e.g., time and travel burdens), scalable approaches for increasing physical activity in this population
are needed to address high rates of inactivity, and related risk of chronic disease and mortality. Fully-
automated Internet programs have potential for increasing physical activity but have rarely been tested in
adults with TKR. Further, it is unknown whether this intervention approach can be scalable and effective in this
population or whether additional enhancements to the program are needed. We propose to use the Multiphase
Optimization Strategy (MOST) framework to identify the optimal intervention components within a scalable,
internet-based physical activity program for adults who are ≥12 months post-TKR. Participants will be recruited
nationwide to participate, and all will receive the core Energize! Exercise Program, a 6-month fully automated
program. Energize! provides a platform for participants to plan and report exercise daily, watch and complete
behavioral video lessons and related homework assignments, and receive brief automated feedback on activity
levels. In addition to Energize!, participants will be randomized to receive 0-4 non-automated supplemental
components, which were selected based upon prior research and guided by the Self-Determination Theory
(SDT) and Supportive Accountability: 1) phone coaching, 2) progress reports sent to physicians/surgeons, 3)
tailored modules specific to adults with TKR, and 4) individualized human feedback (delivered electronically)
on submitted homework assignments. The primary aim is to identify which supplemental intervention
components contribute to the greatest increases in physical activity (total moderate-to-vigorous intensity
physical activity [MVPA] and percent meeting guidelines [≥150 min/week of MVPA]) at 6 and 12 months.
Secondary aims include assessing the effect of the intervention components on pain and physical function and
examining how the core and supplemental intervention components mediate changes in physical activity via
targeted mechanisms: program adherence, SDT targets (autonomy, competence, relatedness), and supportive
accountability. The overarching goal of this study is to build an optimized physical activity intervention for
adults with TKR using the supplemental non-automated components that were found to contribute significantly
to increases in physical activity. Once developed, this optimized intervention can be fully tested in a future trial.
Study findings have the potential to impact clinical practice, as this would represent a translatable model that
could be scaled within healthcare systems for adults with TKR.